The Effect of Topography and Rye Cover Crop on Soil Nitrate Dynamics in a Corn-Soybean Rotation.

Excess nitrate present in the soil either during or after the growing season poses the risk of nitrate entering waterways either via runoff or deep percolation, and resulting in eutrophication of surface waters. As such, nitrate from agricultural sources poses a significant environmental risk. The objective of this study is to examine possible mitigation strategies in this context. Methods involve examining the effects of three topographical positions (summit, slope, and depression) and the use of a rye cover crop on soil nitrate dynamics in a corn-soybean rotation in the United States Midwest, using a crop simulation modeling approach. Continuous soil moisture, several crop parameters throughout the growing season, and weather data were collected from two experimental locations over a two-year period for specific use with the DSSAT crop simulation model, with the intent to (1) examine how soil nitrate varies with topography and (2) how the use of a rye cover crop influences nitrate dynamics. Initial results indicate that early spring surface soil nitrate (5cm depth) was lower in plots with a rye cover crop than in fallow plots. Also, all depression plots tended to have overall higher soil moisture at depths below 40cm, while depression plots without cover crops showed higher nitrate content at 60cm depth. Therefore, nitrate dynamics appear to vary with a combination of soil moisture content (as expressed in topography), as well as the presence of a rye cover crop.